Hard Hot Start With Air Cleaner Installed

[Danny Cabral]

I know it's an old topic, but 20 lbs/hr Cranking Fuel hot seems like a lot, because I've got only 4.5 on mine.

4.5 lbs/hr Cranking Fuel (hot) may be enough for smaller engines, but it's not enough on larger engines. My Cranking Fuel is 9 lbs/hr at 180°F & higher. Also, ensure the "Actual System Pressure" parameter is correctly programmed in Engine Parameters. If it's not, the lb/hr values will be inaccurate (throughout the EFI software).

[Sponge]

20 lbs/hr from -20°F − 80°F
18 lbs/hr at 100°F
16 lbs/hr at 120°F
7.3 lbs/hr at 140°F
5.7 lbs/hr at 160°F
4.5 lbs/hr at 180°F − 260°F

So I'm asking if my "After Start Enrichment" is not too high: 114 from 140°F till 260°F. If I understand those figures well; the Decay Rate is the number of seconds it takes to "spray" the additional percentage in the "After Start Enrichment"? For example, 114% means it takes xx seconds to spray 14% of what? Cranking Fuel?

[Danny Cabral]

If I understand those figures well; the Decay Rate is the number of seconds it takes to "spray" the additional percentage in the "After Start Enrichment"?

EFI Software Help Information/Instructions:
‒ On the top Toolbar, click "Help" & "Contents". This opens all Help topics.
‒ When navigating the software, click "Help ?", drag it to any parameter and click again.
..This automatically opens the definitions for that specific parameter.
‒ Tuning information can be read by clicking the F1 key, when you're viewing any screen.
http://documents.holley.com/techlibr...10555rev17.pdf (Holley EFI Wiring Manual & Diagrams)
http://documents.holley.com/techlibrary_199r10544.pdf (Holley EFI Help/Instructions Overview)
http://forums.holley.com/showthread....ents-Read-This! (Initial Checks & Adjustments - Read This!)

In the "Help" Contents of the EFI software (Step-By-Step Beginner's Tuning), look at the "Idle Fuel vs. Temperature" graphical representation - Figure 8, Section 5.1.
Under 400 RPM (the "Crank To Run RPM"), the ECU only looks at the Cranking Fuel (lb/hr) Table, the Cranking Timing value, and the IAC Parked Position %.

Cranking Fuel & After Start Enrichment are not the same thing. Cranking Fuel only happens during cranking. When the engine starts, the After Start Enrichment is injected for a brief period of time (After Start Enrichment Time - Decay Rate). The After Start Enrichment fuel is a modifier (%) of the Base Fuel Table, based on coolant temperature. The After Start Decay Rate (linear decay to zero) is the time duration of the After Start Enrichment in seconds.

[andrewb70]

I'm trying to optimize my hot starting as well. To me, it seems that the engine should fire up very clean & crisp when hot, and mine just doesn't. With respect to Cranking Fuel, wouldn't this number be similar to the fuel flow rate at idle? Andrew

[Danny Cabral]

With respect to Cranking Fuel, wouldn't this number be similar to the fuel flow rate at idle?

On some engines, it is a good hot starting point (see post #6). Some engines like more Cranking Fuel. Try it both ways and see which amount your engine likes. Also, some engines don't tolerate a lot of "Fuel Prime Percent" on hot restarts.

[andrewb70]

Thanks Danny. I'll play around with it some, after I get some wiring work redone. Andrew

[Danny Cabral]

You already know this; it's about tuning air, fuel & timing. We addressed fuel in post #17. Ensure your throttle blades are adjusted far enough open. Try 10° or 15° of Cranking Timing.
http://forums.holley.com/showthread....7913#post77913 (Related Cranking/Startup Tuning Post)

[andrewb70]

Wanted to close the loop on this. I've had my IAC Parked Position at 38%, and my Cranking Fuel around 3.5 lb/hr, and I had the Fuel Prime set to 100%. I noticed that it seemed to fire up a little faster if I bumped up the IAC Parked Position to 50%. I then upped the Cranking Fuel to 4.5 lb/hr, and changed the Fuel Prime to 150%. Now it fires up almost instantly! Andrew

[Danny Cabral]

Now it fires up almost instantly!

Congratulations. That's what tuning is all about. My (hot) IAC Parked Position is also 50%.

[V8Billy]

What's the Fuel Prime Percent a percent of? Currently using 100% for the Fuel Prime, although I'm not sure what it is 100% of. As for starting without an IAC, do you have any recommendations for settings?